1. Field of the Invention
The present invention relates to a cleaning machine for cleaning objects such as semiconductor wafers and a method of controlling the same.
2. Description of the Related Art
In a cleaning process of the manufacturing steps of a semiconductor device such as LSI, a cleaning machine has been conventionally used to remove contaminations such as particles formed on a semiconductor wafer, organic contaminants, metallic impurities. Particularly, a wet-type cleaning machine has been widely used since particles can be effectively removed and a batch process can be carried out.
In the wet-type cleaning machine discussed above, a containing member, which is called a carrier, containing a predetermined number of semiconductor wafers, e.g., 25 semiconductor wafers, is loaded on a loader of the cleaning machine by a transfer robot. After an orientation flat alignment is carried out and the contained semiconductor wafers are lifted up from the carrier by a holding unit so that the lifted-up semiconductor wafers are set to a transfer standby state. The semiconductor wafers in the transfer standby state are transferred to a cleaning section where various kinds of cleaning processes are carried out by a transfer machine having a chucking unit, which is called a wafer chuck. Then, in the cleaning section, a predetermined cleaning process is provided to the semiconductor wafers.
The cleaning section comprises one or more cleaning units, which are sequentially arranged to carry out various kinds of chemical cleaning such as SC1 cleaning, S2 cleaning, HF cleaning, and SPM cleaning. Each of the cleaning units comprises a chemical liquid cleaning bath for chemical liquid cleaning and a water cleaning bath for pure (deionized) water cleaning. Processing objects transferred by the transfer machine are cleaned with chemical liquid in the chemical liquid cleaning bath to be supplied to the water cleaning bath provided at a lower stream of the chemical cleaning bath. In the water cleaning bath, chemical liquid adhered onto a surface of each of the semiconductor wafers is washed off with pure water so as to be transferred to a cleaning unit using a different kind of chemical liquid. In this way, a series of cleaning processes is ended, and the wafers are finally cleaned with pure water. Then, the finally cleaned wafers are dried, and transferred to an outer section of the cleaning machine through an unloader section.
In the chemical liquid cleaning bath of the above-mentioned cleaning machine, there are generally used chemical liquids having high temperature and high reactivity such as APM (mixture of aqueous ammonia and hydrogen peroxide), HPM (mixture of hydrochloric acid and hydrogen peroxide), HF (hydrofluoric aqua) or SPM (sulfuric acid). Due to this, there is the possibility that a lot of wafers to be processed will be damaged or that the cleaning machine itself may be in a dangerous state in some cases, e.g., abnormality of chemical liquid itself such as abnormality of temperature or that of an amount of chemical liquid, trouble with the chemical liquid cleaning bath itself, for example, abnormality of the chemical liquid circulating system, that of an exhaust system, or that of an opening/closing mechanism of a cover.
Therefore, regarding the trouble of the chemical liquid cleaning bath, it is important for the cleaning machine itself to be controlled to be automatically avoid the worst state based on a fail-safe concept. Due to this, development of the cleaning machine and its control system has been strongly desired.
In the chemical liquid cleaning bath, there is possibility that various kinds of trouble will be generated at the time of the cleaning process. For example, if the temperature of chemical liquid is too low, processing objects cannot be sufficiently cleaned. If the temperature of chemical liquid is too high, there is the possibility that damage is exerted onto normal portions excepting the portion where contaminants are adhered. Also, if chemical liquid is not sufficiently supplied to the chemical liquid cleaning bath, there is possibility that damage will be exerted on a wafer portion exposed to air in addition to the point that the wafers are cannot be sufficiently cleaned. Furthermore, if the amount of chemical liquid in the chemical liquid cleaning bath is too large, there is possibility that the structural parts of the chemical liquid cleaning bath will be damaged or contaminated. In the cleaning machine, an exhaust mechanism is provided to exhaust vaporized chemical liquid. However, if trouble occurs in such an exhaust mechanism, there is possibility that vaporized chemical liquid will not be sufficiently exhausted so that the structural parts of the chemical liquid cleaning bath will be damaged or contaminated. Or, even in a case where abnormality occurs in the chemical circulating system, the wafers cannot be sufficiently cleaned. On the chemical liquid cleaning bath, a cover is provided. The cover is opened when the wafers are place in or taken out of the bath, and closed when the wafers are neither taken in nor placed out. Thereby, chemical liquid can be prevented from being diffused from the chemical liquid cleaning bath. Also, contaminants can be prevented from being introduced to the chemical liquid cleaning bath from the outer section. However, if trouble occurs in the opening/closing mechanism of the cover, there is the possibility that the wafers of the chemical liquid cleaning baths will be taken out and that the wafers will be damaged.